1. Field
This disclosure is generally related to a sputtering system used for fabricating solar cells. More specifically, this disclosure is related to a radio frequency (RF) sputtering system equipped with a rotary target.
2. Related Art
Anti-reflection coatings (ARCs) play an important role in ensuring high efficiency of silicon-based solar cells because the bare Si has a high surface reflection rate. Most ARCs include one or more layers of dielectrical material, such as SiO2, SiNx, etc. Moreover, many solar cells also include a thin layer of transparent conducting oxide (TCO) material (such as indium-tin-oxide (ITO) or indium doped zinc oxide (ZIO)), which may also act as an ARC layer, on their top surface to ensure good ohmic contact between the metal electrode and the underlying Si layers.
Among various film deposition techniques, sputtering has been widely used by solar cell manufacturers as a tool for depositing the ARC and/or TCO layers because it can provide a high-quality film with sufficiently low interface defect density (Dit), which is important for achieving high-efficiency solar cells. However, currently available sputtering systems for manufacturing PVDs often rely on applying a high direct-current (DC) voltage to the target, and may result in a charge build-up on floating-potential surfaces and arcing. The occurrence of arcing makes the plasma and the deposition process unstable and therefore unpredictable. To decrease the influence of the arcing effect, alternating voltages can be used to prevent charge build-up at the floating-potential surface. However, DC-pulsed sputtering usually cannot meet the low-damage requirement of high-efficiency solar cells.